An organic compound, which has relative volatility of one or greater at room temperature, relative to water, is considered to be a volatile organic compound (VOC). The VOCs and petroleum hydrocarbons are among the most commonly cited organic ground water contaminants. Some of the VOCs are toxic and have been classified as carcinogens. Of particular concern are chlorinated ethylenes, such as trichloroethylene (TCE); tetrachloroethylene, commonly known as perchloroethylene (PCE); and chlorinated ethanes, such as 1,1,1-trichloroethane, which have been used as degreasing solvents for petroleum oils and in a variety of industrial applications. As analytical detection limits have improved, trace amounts of the VOCs (in fractions of a part per billion) have been detected in many water supplies, causing public concern. Although the use of TCE was severely curtailed in 1976, its improper storage and uncontrolled disposal practices resulted in significant TCE contamination of ground water aquifers. Due to its high solubility in water (100 parts per million @25.degree. C.), TCE is highly mobile in soils and water aquifers.
Petroleum spills and leaky underground storage tanks also contribute significantly to ground water contamination. Petroleum products are a complex mixture of hundreds of chemicals, generally having paraffin and naphthalene based hydrocarbons. Petroleum products are generally lighter than water and tend to float above the ground water table.
Similarly due to increasingly stringent clean air regulations, flue gases generated by various chemical industries have to be stripped of the VOCs before they are released into the atmosphere.
Air stripping has proven to be one of the most practical techniques for removing the VOCs from groundwater. By pumping contaminated groundwater through an air stripping tower, many of the VOCs can be removed efficiently at reasonable capital and operating costs. A well-designed system can exceed 99.9% removal of many of the VOCs including benzene, toluene, TCE, PCE, chloroform, methylene chloride, carbon tetrachloride as well as ethylbenzene and xylene (BTEX) contained in gasoline. The process can be designed to simultaneously treat combined contaminations that result from multiple spills and leaks of different chemicals into the groundwater.
In order to meet the required air quality standards, the VOCs transferred to air by the air stripper have to be removed before air is vented to the atmosphere. Some of these processes are disclosed in Reduction of Volatile Organic Compounds in Aqueous Solutions Through Air Stripping and Gas-Phase Carbon Adsorption by Fang, C. S. and Khor, Song-Leng in Environmental Progress (Vol. 8, No. 4), November 1989, pages 270-278 and Vapor-phase adsorption cuts pollution, recovers solvents by Parmele, Charles S.; OConnell, Wilbert L. and Basdekis, Harold S. in Chemical Engineering, Dec. 31, 1979, pages 58-70. State-of-the-art treatment methods include incineration and activated carbon adsorption. However, both technologies suffer from significant shortcomings. Direct incineration of air streams containing small amounts of organic contaminants is technically feasible, but expensive owing to the large volumes of air that have to be treated. Concentration of the VOCs by carbon adsorption/desorption suffers from a number of serious limitations including low adsorption capacity, sensitivity to the presence of water and water vapor, high temperature regeneration/reactivation, high loss of carbon by attrition and thermal decomposition during regeneration, accumulation of nondesorbables and corrosion caused by HCl formed during the decomposition of chlorinated organics. Saunders, Gary L., Carroll, Jr., John P., Dunbar, David R. and Padgett, Joseph, in Cost of Controlling Air Stripper Emissions, Treatment, pages 748-752, conclude that the cost per ton of the VOCs is extremely sensitive to the tons/year of the VOCs adsorbed. Thus, a need exists for providing a regenerative sorption process having a high rate of the VOC sorption.
In addition to carbon adsorbents, a number of carbonaceous adsorbents based on sulfonated styrene/divinylbenzene macroreticular ion exchange resins have been developed. These adsorbents suffer from many of the same disadvantages as carbon adsorbents, including sensitivity to moisture and low adsorption capacity (as low as 5%).
The U.S. Pat. No. 4,764,282 of Snyder, Robert H. is directed to using vulcanized automobile rubber tire scrap for absorbing halogenated hydrocarbon waste, prior to its incineration at suitable sites. However, no means for regenerating sorbed tire scrap is disclosed.
The U.S. Pat. No. 4,519,816 of Clarke, Donald H. is directed to using polyurethane foam for separating the VOCs from air.